Brönsted Basicities and Nucleophilicities of N-Heterocyclic Olefins in Solution: N-Heterocyclic Carbene versus N-Heterocyclic Olefin. Which Is More Basic, and Which Is More Nucleophilic?
作者:Zhen Li、Pengju Ji、Jin-Pei Cheng
DOI:10.1021/acs.joc.0c02838
日期:2021.2.5
common reference electrophiles for quantifying nucleophilic reactivities. In general, the nucleophilicity of the NHOs is much stronger than that of commonly used Lewis bases such as Ph3P or DMAP [4-(dimethylamino)pyridine] but weaker than that of their NHC analogues; however, caution should be taken when generalizing this conclusion to a wide range of electrophiles with distinctively electronic and structural
通过使用紫外可见光谱法测量相应的前体在DMSO中的平衡酸度,建立了包含9种代表性N-杂环烯烃(NHO)的布朗斯台德碱度标度。基本性(p K aH被调查的NHO的s)范围从14.7到24.1。不饱和NHO的碱性比其N-杂环卡宾(NHC)类似物的碱性强。但是,饱和盐的碱度比其NHC类似物的碱度弱得多,这在很大程度上是由于芳香化作用本质上影响NHC和NHO前体的酸离解。通过监测这些NHO与常用参比亲电试剂的反应动力学来光度法测量四个NHO的亲核性,以定量亲核反应性。通常,NHO的亲核性比常用的路易斯碱(例如Ph 3)强得多P或DMAP [4-(二甲氨基)吡啶],但比其NHC类似物弱;然而,将这一结论推广到具有明显电子和结构特性的各种亲电子试剂时,应谨慎行事。
[EN] PHOSPHONIUM IONIC LIQUIDS AS RECYCLABLE SOLVENTS FOR SOLUTION PHASE CHEMISTRY<br/>[FR] LIQUIDES IONIQUES DE PHOSPHONIUM UTILISES EN TANT QUE SOLVANTS RECYCLABLES POUR DES PROCESSUS CHIMIQUES EN PHASE SOLUTION
申请人:UNIV FRASER SIMON
公开号:WO2006007703A1
公开(公告)日:2006-01-26
This application relates to the use of phosphonium-based ionic liquids as recyclable solvents for solution phase chemistry. The ionic liquids may be used, for example, as solvents for reactions involving Grignard reagents, hydridic reagents, metallic and non-metallic reducing agents, and strong bases, including nucleophilic carbenes and Wittig reagents. In one embodiment the invention may comprise homogeneous mixtures of strong bases/nucleophiles/reducing agents and tetrahydrocarbylphosphonium salt ionic liquids. The invention also relates to chemical processes that may proceed in either minimally flammable solvent, or a complete absence of flammable solvent, including systems containing strong reducing agents such as alkali and alkaline metals or metal and non-metal hydrides. Methods for generating anions and nucleophililic carbenes (imidazol-2-ylidenes) (and complexes derived from them) in phosphonium-based ionic liquids are also described. The invention demonstrates the feasibility of using phosphonium-based ionic liquids as a reliable reaction media for a wide variety of basic reagents. The problems associated with C-H activation in imidazolium-based ionic liquids by highly reactive bases are not observed for phosphonium-based ionic liquids.
N-Heterocyclic Olefins as Organocatalysts for Polymerization: Preparation of Well-Defined Poly(propylene oxide)
作者:Stefan Naumann、Anthony W. Thomas、Andrew P. Dove
DOI:10.1002/anie.201504175
日期:2015.8.10
polymerization of propylene oxide (PO) using a special class of alkene—N‐heterocyclic olefins (NHOs)—as catalysts is described. Manipulation of the chemical structure of the NHO organocatalyst allows for the preparation of the poly(propylene oxide) in high yields with high turnover (TON>2000), which renders this the most active metal‐free system for the polymerization of PO reported to date. The resulting polyether
Organocatalysis is employed as a precise tool for the preparation of triblock-copolyethers for a systematic access to structure-direction.
有机催化被用作一种精确工具,用于制备三嵌段共聚醚,以实现对结构定向的系统性访问。
Lewis Pair Polymerization of Epoxides via Zwitterionic Species as a Route to High‐Molar‐Mass Polyethers
作者:Patrick Walther、Annabelle Krauß、Stefan Naumann
DOI:10.1002/anie.201904806
日期:2019.7.29
used to prepare poly(propylene oxide) with a molar mass (Mn) >500 000 g mol−1, in some cases even >106 g mol−1, as determined by GPC/light scattering. This is achieved by combining the rapid polymerization characteristics of a zwitterionic, Lewispair type mechanism with the efficient epoxide activation by the MgII species. Transfer‐to‐monomer, traditionally frustrating attempts at synthesizing polyethers
使用基于N杂环烯烃(NHOs)和双(六甲基二硅叠氮化镁)(Mg(HMDS)2)的双催化装置制备摩尔质量(M n)> 500 000 g mol -1的聚环氧丙烷通过GPC /光散射测定,在某些情况下甚至大于10 6 g mol -1。这是通过将两性离子路易斯对型机理的快速聚合特性与Mg II的有效环氧化物活化相结合而实现的物种。传统上阻碍合成高聚合度的聚醚的传统尝试是转移单体,但实际上已被这种方法作为限制因素而取消。NMR和MALDI-ToF MS实验揭示了所提出机制的关键方面,由此聚合反应是由NHO通过对活化单体的亲核攻击而引发的,从而生成两性离子物质。该策略也可以扩展到其他环氧化物,包括功能化单体。